Fix OTel Appender for tracing from suppressing other layers

[cijothomas]

Fixes #1682

No change in performance.
Also modified benchmarks to remove the need of a noop exporter, as noop processor is sufficient to test perf for enabled/disabled. (This change has no perf impact even without this cleanup.)

[codecov]

Codecov Report

Attention: Patch coverage is 88.88889% with 1 line in your changes missing coverage. Please review.

Project coverage is 79.1%. Comparing base (41b381a) to head (63e1b95).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
opentelemetry-appender-tracing/src/layer.rs	88.8%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #2668     +/-   ##
=======================================
- Coverage   79.1%   79.1%   -0.1%     
=======================================
  Files        122     122             
  Lines      22562   22560      -2     
=======================================
- Hits       17861   17858      -3     
- Misses      4701    4702      +1     

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[lalitb]

Thanks for fixing this.